String+与StringBuffer.append()的速度比较

StringBuild的比较，代码如下：

public class Test {
 public static void main(String[] args)
 {
  String a = "a";
  String b = "b";
  String c = "c";
  long start = System.currentTimeMillis();
  for (int i = 0; i < 100000000; i++) {
String string = a + b + c;
if (string.equals("abc")) {}
  }
  System.out.println("string+ cost time:" + (System.currentTimeMillis() - start) + "ms");
  start = System.currentTimeMillis();
  for (int i = 0; i < 100000000; i++) {
StringBuffer stringBuffer = new StringBuffer();
stringBuffer.append(a);
stringBuffer.append(b);
stringBuffer.append(c);
String string = stringBuffer.toString();
if (string.equals("abc")) {}
  }
  System.out.println("stringbuffer cost time:" + (System.currentTimeMillis() - start) + "ms");
  start = System.currentTimeMillis();
  for (int i = 0; i < 100000000; i++) {
StringBuilder stringBuilder = new StringBuilder();
stringBuilder.append(a);
stringBuilder.append(b);
stringBuilder.append(c);
String string = stringBuilder.toString();
if (string.equals("abc")) {}
  }
  System.out.println("stringbuilder cost time:" + (System.currentTimeMillis() - start) + "ms");
 }
}

结果如下：

正如上面文章所说，此处的String其实调用的两次StringBuild的append()方法，相较于后两种都是更快的。

结论：在string+写成一个表达式的时候（更准确的说，是写成一个赋值语句的时候），效率其实比另两个更快，但如果不是这样的话，则效率会明显低于另外两个。